A heat pipe has a surface thermal conductance several to several ten times as high as that of copper and aluminum, and is therefore an excellent cooling device often employed in heat-removing related apparatus. According to its shape, the heat pipe can be generally divided into a round heat pipe and a plane heat pipe. For cooling a heat-producing element in an electronic device, such as a central processing unit (CPU), the plane heat pipe is more suitable for use to dissipate heat because it can be more easily mounted on and have a larger contact area with the heat-producing element. Due to the demands for miniaturized cooling mechanism to save space, it becomes absolutely necessary to develop a heat pipe with extremely low profile. Therefore, a thin heat pipe, i.e. a flat plate heat pipe, has been developed by related manufacturers.
A conventional thin heat pipe has an internal space for receiving a working fluid therein and used as a flow passage for the working fluid. When the working fluid in the thin heat pipe is heated at a vaporizing end thereof and changes from a liquid phase into a vapor phase and therefore flows from the vaporizing end to an opposite condensing end of the thin heat pipe, heat produced by a heat-producing element is transferred via the thin heat pipe from the vaporizing end to the condensing end to achieve the heat transfer and dissipation effect.
To manufacture the conventional thin heat pipe, a type of metal powder is filled in a hollow pipe. The metal powder is sintered to form a wick structure layer on inner surfaces of the hollow pipe. The hollow pipe is then evacuated and filled with a working fluid before being flattened to form a thin heat pipe structure.
While the conventional thin heat pipe has a relatively low profile, it has another problem to be solved. That is, the vaporizing end and the condensing end of the conventional thin heat pipe have the same pipe size, so that the spaces in the vaporizing end and the condensing end are also the same in volume. With this design, there is almost little pressure difference between the spaces of the vaporizing end and the condensing end. As a result, the vapor-phase working fluid can not quickly flow from the vaporizing end to the condensing end for cooling and converting into the liquid phase, which in turn adversely affects the rate at which the liquid-phase working fluid flows from the condensing end via the wick structure back to the vaporizing end. Therefore, the vapor-liquid circulation in the whole thin heat pipe is poor and there is no way to solve the problem of pressure resistance between the vaporizing end and the condensing end of the thin heat pipe.
In addition, when the conventional thin heat pipe is bent during the manufacturing process, the sintered wick structure layer inside the thin heat pipe is brittle and tends to break or separate from the inner surfaces of the thin heat pipe, rendering the thin heat pipe a defective product having largely lowered heat transfer performance.
In brief, the conventional thin heat pipe has the following disadvantages: (1) having poor vapor-liquid circulation efficiency; (2) providing low heat transfer and dissipation performance; and (3) failing to solve the problem of high pressure resistance between the vaporizing end and the condensing end of the thin heat pipe.
It is therefore tried by the inventor to develop an improved thin heat pipe structure to overcome the disadvantages in the conventional thin heat pipe.